A181654 An eigentriangle of the number triangle A181653.

1, 1, 1, 2, 1, 1, 3, 2, 1, 1, 6, 4, 2, 1, 1, 9, 6, 3, 2, 1, 1, 18, 12, 6, 4, 2, 1, 1, 27, 18, 9, 6, 3, 2, 1, 1, 54, 36, 18, 12, 6, 4, 2, 1, 1, 81, 54, 27, 18, 9, 6, 3, 2, 1, 1, 162, 108, 54, 36, 18, 12, 6, 4, 2, 1, 1

Offset

0,4

Comments

Generalized (conditional) Riordan array with k-th column generated by x^k*if(mod(k,2)=0,(1+x-x^2)/(1-3x^2),(1+x-x^2+x^3)/(1-3x^2)).

Row sums are A181655.

Links

Table of n, a(n) for n=0..65.

Paul Barry, Invariant number triangles, eigentriangles and Somos-4 sequences, arXiv preprint arXiv:1107.5490 [math.CO], 2011.

Example

Triangle begins
1,
1, 1,
2, 1, 1,
3, 2, 1, 1,
6, 4, 2, 1, 1,
9, 6, 3, 2, 1, 1,
18, 12, 6, 4, 2, 1, 1,
27, 18, 9, 6, 3, 2, 1, 1,
54, 36, 18, 12, 6, 4, 2, 1, 1,
81, 54, 27, 18, 9, 6, 3, 2, 1, 1,
162, 108, 54, 36, 18, 12, 6, 4, 2, 1, 1

Crossrefs

Sequence in context: A049286 A308477 A079216 * A323756 A192710 A316831

Adjacent sequences: A181651 A181652 A181653 * A181655 A181656 A181657

Keyword

easy,nonn,tabl

Author

Paul Barry, Nov 03 2010

Status

approved